Several matrices can be associated to a graph such as the adjacency matrix or the Laplacian matrix. The spectrum of these matrices gives some informations about the structure of the graph and the question “Which graphs are determined by their spectrum?” remains a difficult problem in algebraic graph theory. In this article we enlarge the known families of graphs determined by their spectrum by ...

-Monthly values of el0, the critical frequency relative to the critical frequency at zero sunspots, have been averaged for a number of stations and tabulated for the eleven-year period 1937-47. The variations of el0 for the E-, Fi-, and F2-regions have been correlated with the solar data for sunspot-numbers, bright Ha and Ca floecult, faculae, and the coronal-line intensity. The variations corr...

Surfaces of the Sun and other cool stars are filled with magnetic fields, which either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection characterisation exoplanets, affecting stellar brightness spectra, well transmission spectra. However, expected facular spot signals in data quite different, for instance they have distinct temporal spectral profi...

In the middle of seventeenth century, Andr\'e Tacquet, S.J. briefly discussed a scientific argument regarding structure Copernican universe, and commented on Galileo Galilei's discussion that same -- Galileo's in turn being commentary version by Christoph Scheiner, The was based observations sizes stars. This exchange involving two Jesuits illustrates how through much science meaning measuremen...